(i) Angioplasty and Conventional Dilatation Catheter Systems.
Over the last decade the medical procedure known as angioplasty has become widely accepted as a safe and effective method for treating various types of vascular diseases. For example, angioplasty is widely used for opening stenoses throughout the vascular system and particularly for opening stenoses in coronary arteries. At present, the most common form of angioplasty is called percutaneous transluminal coronary angioplasty (PTCA). This procedure utilizes a dilatation catheter having an inflatable balloon at its distal end. Using a fluoroscope and radiopaque dyes for visualization, the distal end of the dilatation catheter is guided into position through a guide catheter and across the stenosis and the balloon is inflated for a brief duration to open the artery and establish adequate blood flow. Typically, inflation of the balloon is accomplished by supplying pressurized fluid through an inflation lumen in the catheter which is connected to an inflation apparatus located outside the patient's body. Conversely, applying a negative pressure to the inflation lumen collapses the balloon to its minimum dimension for initial placement or removal of the balloon catheter within the target blood vessel.
A number of balloon catheter designs have been developed which have contributed to the safety and acceptability of PTCA and similar medical procedures. The most common design is known as an "over-the-wire" balloon catheter. This device typically utilizes a relatively large lumen for passage of a guide wire and injection of angiographic visualization dye to assist in the placement of the device. In some cases, a second parallel lumen is provided for inflation and deflation of the balloon, such a design commonly referred to as a "dual lumen" design. Alternatively, instead of a second lumen, the wall of the catheter body itself defines an open space between the catheter body and the guidewire lumen for allowing inflation media to pass therethrough. This is commonly referred to as a "coaxial" design. Typically, a steerable guide wire is positioned within the larger lumen and the entire assembly is maneuvered into an initial position within the target artery through a previously positioned large diameter guide catheter. Once near the site of the stenoses the guide wire can be rotated and axially extended or retracted into position across the lesion. The catheter is subsequently advanced along the guide wire to position its balloon end across the lesion prior to inflation of the balloon and dilatation of the stenosis.
An alternative over-the-wire catheter assembly utilizes a non-removable or fixed guide wire that allows for longitudinal or axial movement. However, this design has a significant drawback because the entire non-removable guide wire catheter assembly must be removed to accomplish replacement or exchange of the balloon. In some cases of PTCA it is necessary to replace the balloon with one of different diameter or configuration following the initial dilatation. Additionally, cases of acute reclosure have been noted where the lesion recloses following dilatation and removal of the balloon catheter. This alternative system increases the difficulties of these subsequent procedures by requiring that the replacement catheter renegotiate the entire placement path without the advantage of a guide wire.
A "monorail" or "rapid exchange" variant of the standard balloon-over-a-wire system also has been developed where only the distal portion of the balloon catheter tracks over the guide wire. This system utilizes a conventional inflation lumen and a relatively short guiding or through lumen at the distal end. Its principal benefits are the reduction of frictional drag over the length of the externally located guide wire and the ease of balloon exchange. It provides the ability to recross an acutely closed vessel or to exchange balloons without removing the guide wire.
Another dilatation catheter design is the "fixed-wire" or integrated "balloon-on-a-wire" dilatation catheter. These single lumen designs utilize a relatively narrow wire positioned within the inflation lumen and permanently fixed to the distal end of the balloon. This produces a low-profile assembly which is able to cross severely narrowed lesions and to navigate tortuous vascular pathways. Additionally, the fixed guide wire bonded at the distal end of the balloon improves the steerability and pushability of these designs which enhances their maneuverability. The thin shaft design also improves coronary visualization and enables all but the tightest critical lesions to be crossed. However, though able to provide relatively quick and simple balloon placement as well as providing access to lesions otherwise unsuitable for PTCA, fixed-wire systems sacrifice the ability to maintain guide wire position across the lesion when exchanging balloons or the safety advantage of being able to recross an acutely closed vessel without repositioning the entire assembly.
(ii) The Need for Catheter Exchange.
In many angioplasty procedures, it may become necessary to exchange catheters. There are many reasons which may require such catheter exchange. For example, the balloon catheter may malfunction, a larger balloon may be required to further dilate the vascular stenoses, another device may be needed to remove vascular material, and so on. In each of these situations, the original dilatation catheter must be removed, and a new dilatation catheter must be used. It is estimated that about half of the angioplasty procedures require the use of more than one dilatation catheter.
The use of two or more dilatation catheters significantly increases the cost to both the patient and the hospital. For example, the patient must pay for the cost of an additional dilatation catheter; the hospital must stock a larger inventory of dilatation catheters, which requires more storage space; and more packaging components are required, which increases the amount of waste or recyclable matter. All the above factors also result in greater administrative attention and expense.
Thus, there remains a need for a dilatation catheter assembly that is cost-efficient, is easy to use, and is easy to manufacture.